It is well known that a polypropylene resin is blended with an elastomer, e.g., ethylene/propylene or ethylene/butene copolymer, to improve its impact resistance.
However, blend of the elastomer led deterioration in rigidity of the polypropylene resin, therefore there is a limit in the amount of the blended elastomer. A formed resin article, e.g., that of polypropylene resin, may be required to have impact resistance both at normal temperature and low temperature. Impact resistance at low temperature may not always correspond to that at normal temperature. Blend of a soft rubber as the modifier may be one method for improving impact resistance at low temperature. However, blend of the soft rubber with a polypropylene resin leads rigidity of the formed article to deteriorate and causes the same problem as above.
Therefore, the modifier capable of keeping the resin in which it is blended well balanced with respect to rigidity and impact resistance has been in demand. On the other hand, a formed resin article, e.g., that described above, is also required to be difficult to fracture under service conditions, by which is meant that it is required to have a high tensile breaking point strength and impact strength while keeping a high rigidity. In other words, the resin modifier capable of keeping the resin in which it is blended well balanced with respect to rigidity and tensile breaking elongation has been also in demand.
Japanese Patent Laid-Open Publication No. 192500/1994 discloses a composition having well-balanced rigidity and impact resistance by incorporating a polypropylene polymer with an ethylene/α-olefin copolymer of specific properties. However, this composition is insufficient in the balances between rigidity and impact strength at low temperature and between rigidity and tensile elongation properties, and is required to be further improved.
Moreover, when modifying resin, some resin modifiers for the above-described resins cause problems, e.g., blocking during the kneading process at a supply section of the kneader, e.g., hopper, to deteriorate productivity and unstable properties of the modified resin.
Therefore, development of the resin modifier capable of improving properties of polypropylene or other resins, in particular tensile breaking point elongation and impact resistance at low temperature, while keeping its rigidity, and, at the same time, causing little problems, e.g., blocking, and excellent in productivity and workability has been keenly demanded.
The inventors of the present invention have already proposed specific compositions of [A] a copolymer of ethylene and α-olefin o 4 to 20 carbon atoms, [B] a copolymer of ethylene and α-olefin if 3 to 20 carbon atoms and [C-1] a high-density polyethylene, as the modifiers which can satisfy the above requirements (Japanese Patent Laid-Open Publication No. 273563/1998. However, these compositions cannot always give the modified resin of well-balanced impact resistance and bending modulus of elasticity.